Janet Frame is a laureate of the musing inner self, her novels made up of relentless soliloquies from the distressed, conveyed in multi-metaphored prose. Her stories of family turmoil, of traumas dwelt upon, have led her to be defined, as the publisher's blurb on this massive biography by Michael King does, as a writer-cum-self-help-guru, a woman who 'climbed out of an abyss of unhappiness to take control of her life'.

Born in New Zealand in 1924, to a family fallen from relative prosperity to ramshackle impecuniousness, she spent her twenties in mental asylums in New Zealand and London, diagnosed as schizophrenic. Her novels, which include Owls do Cry (1957), Faces in the Water (1961) Scented Gardens for the Blind (1963) and Intensive Care (1970), are relentless sagas of distress. The Frame sisters - Janet, June, Myrtle and Laura - felt themselves to be like the Brontës - because they held, by right, 'silk purses' of words, and because their family was an anvil on which disasters fell.

They grew up in cramped rooms in Dunedin; their father a train driver, their mother a housewife and poet. With brother Geordie - doomed by their Brontë myth to Branwellesque decline - they muddied their faces and blotted the neighbourhood with shrieked obscenities. Geordie became an epileptic and, eventually, a wife-smashing alcoholic; Myrtle and Laura died in strange swimming accidents. These events, King suggests, precipitated Frame's mental collapse, and formed much of the matter of her work, in transmuted form.

Just how specifically Frame alludes to family disasters in her disaster-strewn fiction is never resolved in King's elegantly written, densely researched and remorselessly long biography. Frame, while avowing the fictiveness of her accounts of lunacy, also presented her concerns as inward-turning: 'I'm not sure that I see life at all. What I do see is life within.' Faces in the Water she described as 'simply an almost truthful account of a few past experiences'. The first work she referred to explicitly as a novel, The Edge of the Alphabet, was, King writes, 'based on the troubled experience of Geordie'. However, she later suggested that her autobiography, An Angel at my Table, was partly written to convince everyone that, after all 'my fiction is genuine fiction. And I do invent things'.

Frame's definition of autobiography as 'fact', versus fiction as 'invented', is a definition King respects, yet it does not hold the reader. Frame's world beyond this world, her moment of creative rapture, appears to be a point of trance-like introspection.

Yet personal allusions are rendered obscure in Frame's fiction by an intensely metaphorical style. Analogies are laden on to analogies, developing into riots of hyper-meaning. Houses rock 'like a sea', blame rests on individuals 'like a butterfly on a leaf'. One metaphor twirls the paragraph away, into the skewed world of its particular nature, and then is hotly pursued by another, demanding another reality twist. Mental turmoil is described as a 'big brown bird, like a hawk... flying down to pick out my insides, as if I were a sheep or a rabbit and count the jewels in me, to prove everything'. Characters converse with nightmarish apparitions called Uncle Blackbeetle; readers find themselves told at the end of a novel that the narrative has been the deranged fantasy of an incarcerated mute.

In his respectful account, King argues that Frame's strangeness of perception was misdiagnosed as schizophrenia. Her doctors, intercepting letters in which she described gorse smelling like peanut butter, discerned not the artist 'making it new', but the 'disordered mind' confusing a spiky bush with an edible nutty paste. Other psychiatrists, more literary of bent, diagnosed her as a schizophrenic in the manner of 'Van Gogh, of Hugo Wolf'.

Frame was not entirely displeased by these sorts of doctors' notes: 'Great artists, visionaries... My place was set then, at the terrible feast... at least I could endow my work and... life with the mark of my schizophrenia.' What King doesn't suggest, but what haunts the reader, is that Frame's acute depression may have been misdiagnosed as genius. A gulf seems to develop between the hyperbole of eulogies rained upon Frame and her writing. King suggests she was somehow divinely inspired.

From the publication of her first book, The Lagoon and Other Stories (1951), Frame was showered with prizes and plaudits from a commendably generous New Zealand literary establishment. She was sent round the world to expand her mind; later, she was given a deposit for a house. She was feted by the grand old man of New Zealand letters, Frank Sargeson, who became a housewife to her for a year, and gave her a hut to write in. She was put forward for the Nobel Prize; she was compared to Katherine Mansfield and Virginia Woolf. After the plaudits, Frame's poetry disappoints, striking the reader as fridge-magnet disarrangements of words.

Tales of her onomatopoeic word poems about the Holocaust send anticipatory spasms of horror across the solar plexus. Her bons mots fail to delight - her thoughtful definition of 'surrealism' as something 'beyond the real' seems wretchedly sloppy, her analysis of her work draped in lode-star New Ageries: 'I felt those reading it to be within this whirlpool; the whole world with everything broken by the gravity star. Everything was to be renewed - rebuilt, selves, thought, language, everything.'

Such is the meticulousness of King's book that Frame is overexposed. The lustre of genius dims as we read about her driving lessons, fluctuating house prices in Dunedin, her tax returns. Patrick White, writer and Nobel Laureate, wrote Frame a fan letter but refused to meet her, fearing his vision of her as extraordinary would be 'collapsed if she'd crossed the threshold and sat down to tea. He didn't want her to be ordinary... so he fobbed her off'. In King's account, our extended tea party with Frame draws her out as something of an authorial Our Man in Havana, abducted into a plot so wild and extraordinary it constantly resembled fiction.